As a revolutionary invention in the field of lighting in the 21st century, semiconductor lighting has gained a lot of attention from governments, scholars and related institutions worldwide. As for its current development, Gallium Nitride (GaN) based Light Emitting Diodes (LEDs) are the basis for realizing semiconductor lighting. As the technologies of epitaxial growth and chip process advance, internal quantum efficiency and extraction efficiency of GaN-based LEDs have been greatly improved, and luminous efficiency of lighting-class whites is now up to 161 lm/W. Although the luminous efficiency is relatively high, damages to the GaN-based LEDs due to electrostatics are still a serious problem in the application of the GaN-based LEDs. Currently, a common approach to protect a GaN-based LED from electrostatic damages is to connect it in parallel with a Zener diode during encapsulation; however, this would increase encapsulation complexity and manufacture costs. Consequently, a more advantageous approach is to integrate the GaN-based LED structure with an electrostatic protection diode structure in a light emitting device, so that the whole light emitting device is antistatic.
The document “S-J Chang, C-H Chen, Y-K Su, et al., Improved ESD Protection by combining InGaN-GaN MQW LEDs with GaN Schottky diodes, IEEE Electron Device Letters, Vol. 24, No. 3, pp 129-131, 2003” proposed a GaN-based light emitting device integrated with a Schottky diode. FIG. 1a illustrates a sectional view of its structure, and FIG. 1b illustrates an equivalent circuit. With reference to FIG. 1a, the light emitting device includes a GaN-based LED and a GaN Schottky diode. The GaN-based LED structure includes: a sapphire substrate 101; a buffer layer 102, a u-GaN layer 120, an n-GaN layer 103, a multi-quantum well active layer 104, a p-AlGaN barrier layer 105, a p-GaN layer 106 and a transparent conducting layer 111 formed in that order on the sapphire substrate 101; a p-electrode 112 on the transparent conducting layer 111; and, an n-electrode 113 on the exposed n-GaN layer 103. The GaN Schottky diode is formed in the GaN-based LED structure and is electrically isolated by a SiO2 insulation layer 123 from the GaN-based LED structure except the transparent conducting layer 111, the p-electrode 112 and the n-electrode 113. The GaN Schottky diode structure includes: the sapphire substrate 101, the buffer layer 102 on the sapphire substrate 101, the u-GaN layer 120 on the buffer layer 102, an ohmic contact electrode 121 on a part of the u-GaN layer 120, and a Schottky contact electrode 122 on another part of the u-GaN layer 120. The ohmic contact electrode 121 is electrically connected with the p-electrode 112, and the Schottky contact electrode 122 is electrically connected with the n electrode 113. Therefore, the light emitting device is equivalently the GaN-based LED connected in parallel with the GaN Schottky diode, and the equivalent circuit is shown in FIG. 1b. As for the GaN-based LED, when a forward voltage is applied, almost all the current flows through the LED; and when an instantaneous backward electrostatic voltage is applied, it could be discharged through the GaN Schottky diode, i.e., most of the current flows through the Schottky diode, thereby reducing the damage to the GaN-based LED.
However, as the Schottky diode is formed in the LED structure, the conventional antistatic GaN-based light emitting device described above is of great fabrication difficulty and accuracy, and therefore is not suitable for mass production. In order to form the “built-in” Schottky diode, the epitaxial structure has to be etched to the u-GaN layer, which requires a thickened u-GaN layer (otherwise the processing window for etching may be too narrow); however, a thickened u-GaN layer means a cost increase. On the other hand, the presence of the “built-in” Schottky diode takes emitting areas, hence increasing current density of the active area and degrading the luminous efficiency. The case would be even worse while the size of the chip is small.